The objective of our research is to understand the regulation of contraction and relaxation in the muscle cell at the molecular level. Our approach has been to characterize the substructure of the individual fibrous proteins, in particular the myosin molecule, by the techniques of biophysical chemistry and protein chemistry. We plan to continue our studies on the nature of the interactions of the myosin molecule; specifically, those interactions between myosin molecules leading to filament formation, and those interactions between myosin and other proteins leading to contraction and relaxation. The regulatory protein, troponin, will be isolated from a number of different muscles, and the size, shape and function of its subunits determined. The interaction of myosin with the "regulated" actin filament will be investigated in the presence and absence of calcium and/or nucleotide. The role of the minor proteins: C-protein, M-protein and gamma-actinin will also be determined. These solution studies will be coordinated with the work of our associates who are analysing crystalline and other ordered forms of these complex protein systems by X-ray diffraction and electron microscopy.